In the art of advanced high temperature internal combustion engines, studies include having a ceramic cap overlaying the metallic piston so as to protect the piston from the temperature of the burning fuel. This will require a method for adequately bonding the ceramic to the metal such that a high strength joint results. In a similar manner, a high strength bond is required between a ceramic and metal where the metal serves as a heat sink for a rocket nozzle. These are just a few examples of the need for a ceramic-to-metal bond.
The joining of such dissimilar materials has conventionally been accomplished by one of several methods. For the ceramic-metal systems, the conventional joining methods include mechanical fasteners, metal brazing, epoxy resins and epoxy glass bonds. While these methods are adequate for low temperature, low stress applications, they do not produce the type of bond needed for the high temperature, high stress applications as illustrated above. For example, the large difference in coefficients of thermal expansion cause rupture of mechanical joints. Most braze materials melt at about 900 degrees C. The organic-type (resin) epoxy bonds degrade at relatively low temperatures, and some of the bonding materials (e.g., epoxy glass bonds) react chemically with the base materials as the temperature is increased.
Thus, it is a principal object of the present invention to provide an improved method of joining a ceramic shape to a metallic shape.
It is another object to provide a method of joining a ceramic to metallic shape to overcome thermal expansion mismatches between the ceramic and the substrate.
It is also an object of the present invention to provide a bond between a ceramic shape and a metallic shape that eliminates chemical incompatibility among the components.
A further object of the invention is to provide a method for joining a ceramic shape to a metallic shape wherein the weakest portion of the resultant joint is equal to the strength of the weaker material being bonded.
These and other objects of the present invention will become apparent upon a consideration of the following drawings and a detailed description thereof.